Re: [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550: Ensure FIFO Polled Mode

["Duran, Leo" <leo.duran@amd.com>]

Hi Star,
Please see my replies below.

Thanks,
Leo

> -----Original Message-----
> From: Zeng, Star [mailto:star.zeng@intel.com]
> Sent: Wednesday, June 06, 2018 4:07 AM
> To: Duran, Leo <leo.duran@amd.com>; Dong, Eric <eric.dong@intel.com>
> Cc: edk2-devel@lists.01.org; Zeng, Star <star.zeng@intel.com>
> Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Hi Leo,
> 
> I am ok with the code change.
> I was just curious about the motivation for the change.
> 1. No real issue met, but just to follow the doc 8.4.2 ?
> 2. Real issue met, then what is the issue ?
[Duran, Leo] Real issue met (Please see answer to next questions).

> 3. What is the default value of IER for your case ?
[Duran, Leo] Don't care : the state machine in 16550 model required clearing IER to enter FIFO Polled mode.

> 
> If the information are valuable, then they can be added into the commit
> message for further easy maintenance.
> 
> -----Original Message-----
> From: Duran, Leo [mailto:leo.duran@amd.com]
> Sent: Wednesday, June 6, 2018 9:05 AM
> To: Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: RE: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> Ensure FIFO Polled Mode
> 
> Hi Star,
> 
> I came across a 16550 model (simulation) which required clearing IER, and it
> seems that's allowed in the 16650 spec, as noted here:
> http://www.ti.com/lit/ds/symlink/pc16550d.pdf
> 
> 8.4.2 FIFO Polled Mode Operation
> With FCR0=1 resetting IER0, IER1, IER2, IER3 or all to zero puts the UART in the
> FIFO Polled Mode of operation.
> 
> Thanks,
> Leo.
> 
> > -----Original Message-----
> > From: Zeng, Star [mailto:star.zeng@intel.com]
> > Sent: Tuesday, June 05, 2018 7:43 PM
> > To: Duran, Leo <leo.duran@amd.com>; Dong, Eric <eric.dong@intel.com>
> > Cc: edk2-devel@lists.01.org; Zeng, Star <star.zeng@intel.com>
> > Subject: RE: [edk2] [PATCH]
> MdeModulePkg/Library/BaseSerialPortLib16550:
> > Ensure FIFO Polled Mode
> >
> > It will be better to have the information that may could be added into
> > the commit message.
> >
> > 1. Did you meet real issue without this patch?
> > 2. what is the default value of IER in your case?
> >
> >
> > Thanks,
> > Star
> > -----Original Message-----
> > From: Duran, Leo [mailto:leo.duran@amd.com]
> > Sent: Wednesday, June 6, 2018 5:21 AM
> > To: Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>
> > Cc: edk2-devel@lists.01.org
> > Subject: RE: [edk2] [PATCH]
> MdeModulePkg/Library/BaseSerialPortLib16550:
> > Ensure FIFO Polled Mode
> >
> > Any updates on this patch?
> >
> > Do you require to know my "default value of IER"?
> >
> > Thanks,
> > Leo.
> >
> > -----Original Message-----
> > From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of Duran,
> > Leo
> > Sent: Friday, May 25, 2018 8:38 AM
> > To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> > Cc: Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
> > Subject: Re: [edk2] [PATCH]
> MdeModulePkg/Library/BaseSerialPortLib16550:
> > Ensure FIFO Polled Mode
> >
> > Don''t have access to test platform at this time.
> > But will report IER value if I,m able to.
> >
> > Leo
> >
> > Get Outlook for iOS<https://aka.ms/o0ukef>
> > ________________________________
> > From: Zeng, Star <star.zeng@intel.com>
> > Sent: Friday, May 25, 2018 6:13:16 AM
> > To: Duran, Leo; edk2-devel@lists.01.org
> > Cc: Dong, Eric; Zeng, Star
> > Subject: RE: [edk2] [PATCH]
> MdeModulePkg/Library/BaseSerialPortLib16550:
> > Ensure FIFO Polled Mode
> >
> > Reviewed-by: Star Zeng <star.zeng@intel.com>
> >
> > Just a little curious about
> > 1. Did you meet real issue without this patch?
> > 2. what is the default value of IER in your case?
> >
> >
> > Thanks,
> > Star
> > -----Original Message-----
> > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> > Leo Duran
> > Sent: Friday, May 25, 2018 3:08 AM
> > To: edk2-devel@lists.01.org
> > Cc: Dong, Eric <eric.dong@intel.com>; Zeng, Star <star.zeng@intel.com>
> > Subject: [edk2] [PATCH] MdeModulePkg/Library/BaseSerialPortLib16550:
> > Ensure FIFO Polled Mode
> >
> > Put the UART in FIFO Polled Mode by clearing IER after setting FCR.
> > Also, add comments to show DLAB state for registers 0 and 1.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Leo Duran <leo.duran@amd.com>
> > Cc: Star Zeng <star.zeng@intel.com>
> > CC: Eric Dong <eric.dong@intel.com>
> > ---
> >  .../BaseSerialPortLib16550/BaseSerialPortLib16550.c      | 16
> ++++++++++++--
> > --
> >  1 file changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git
> >
> a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> >
> b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> > index 0ccac96..6532c4d 100644
> > ---
> >
> a/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550.c
> > +++
> > b/MdeModulePkg/Library/BaseSerialPortLib16550/BaseSerialPortLib16550
> > +++ .c
> > @@ -3,6 +3,8 @@
> >
> >    (C) Copyright 2014 Hewlett-Packard Development Company, L.P.<BR>
> >    Copyright (c) 2006 - 2016, Intel Corporation. All rights
> > reserved.<BR>
> > +  Copyright (c) 2018, AMD Incorporated. All rights reserved.<BR>
> > +
> >    This program and the accompanying materials
> >    are licensed and made available under the terms and conditions of
> > the BSD License
> >    which accompanies this distribution.  The full text of the license
> > may be found at @@ -30,10 +32,11 @@  //  // 16550 UART register
> > offsets and bitfields  //
> > -#define R_UART_RXBUF          0
> > -#define R_UART_TXBUF          0
> > -#define R_UART_BAUD_LOW       0
> > -#define R_UART_BAUD_HIGH      1
> > +#define R_UART_RXBUF          0   // LCR_DLAB = 0
> > +#define R_UART_TXBUF          0   // LCR_DLAB = 0
> > +#define R_UART_BAUD_LOW       0   // LCR_DLAB = 1
> > +#define R_UART_BAUD_HIGH      1   // LCR_DLAB = 1
> > +#define R_UART_IER            1   // LCR_DLAB = 0
> >  #define R_UART_FCR            2
> >  #define   B_UART_FCR_FIFOE    BIT0
> >  #define   B_UART_FCR_FIFO64   BIT5
> > @@ -554,6 +557,11 @@ SerialPortInitialize (
> >    SerialPortWriteRegister (SerialRegisterBase, R_UART_FCR,
> > (UINT8)(PcdGet8 (PcdSerialFifoControl) & (B_UART_FCR_FIFOE |
> > B_UART_FCR_FIFO64)));
> >
> >    //
> > +  // Set FIFO Polled Mode by clearing IER after setting FCR  //
> > + SerialPortWriteRegister (SerialRegisterBase, R_UART_IER, 0x00);
> > +
> > +  //
> >    // Put Modem Control Register(MCR) into its reset state of 0x00.
> >    //
> >    SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, 0x00);
> > --
> > 2.7.4
> >
> > _______________________________________________
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